Aryl C-H bond functionalization with diphenyldiazomethane induced by rare-earth metal alkyl complexes

The first examples of regioselective aryl ortho-C-H functionalization with diphenyldiazomethane for the construction of C_aryl-N_hydrazinato bonds were accomplished via the activation of C-H bonds and the subsequent reaction of diphenyldiazomethane with the RE-C_aryl bond. The reactions of rare-earth metal monoalkyl complexes LRE(CH₂SiMe₃)(THF)₂ (L = 2,5-[(2-pyrrolyl)CPh₂]₂(N-Me-pyrrole)) supported by a neutral N-methylpyrrole anchored dipyrrolyl ligand with 2 equiv. of Ph₂CN₂ gave irreversibly unprecedented hydrazonato-functionalized imino rare-earth metal complexes LRE(Ph₂CNNC₆H₄-(o-CNHPh) (RE = Y (2a), Lu (2a')) in good yields involving a rather complex process including the interaction of a diazo unit with a RE-C_alkyl bond, a β-H elimination, a N-N cleavage, 1,4-hydrogen transfer and the subsequent C-N coupling with another diphenyldiazomethane. More important is that regioselective aryl C-H bond functionalization with diphenyldiazomethane to construct the C_aryl-N_hydrazinato bonds can be easily achieved by three-component reactions of rare-earth metal monoalkyl complexes, a wide range of substituted imines (including aldimines, ketimines or analogous 2-phenylpyridine) and diphenyldiazomethane, affording various hydrazonato-functionalized phenyl, thienyl imino or pyridyl rare-earth metal complexes 2b-2j at room temperature. A further study indicated that the substituents on the phenyl ring have a great effect on the reaction pathway and governed the C_aryl-N_hydrazinato bond construction. Moreover, the experimental studies show that the formation of the C_aryl-N_hydrazinato bonds is thermodynamically facile, which could be realized at room temperature easily.